<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>计算圆的周长和面积</title>
</head>
<body>
	<div>
        <p>圆的半径：<input id="a" type="text"></p>
        <p>圆的周长：<input id="b" type="text"></p>
        <p>圆的面积：<input id="c" type="text"></p>
    </div>
    
    <script>
        var r = prompt("请输入圆的半径");
        document.querySelector("#a").value = r;
        
        var lone = r;
        var q = Math.PI;
        var b = (r * 2 * q);
        document.querySelector("#b").value = b;
        var c = (q * r)*(q * r);
        document.querySelector("#c").value = c;
    </script>
</body>
</html>